PROJECT SUMMARY The primary hypothesis of this proposal is that co-targeting of already-validated leukemia surface antigens and essential cytokine receptor pathways in genetic subtypes of high-risk pediatric ALL and AML will reduce the emergence of treatment resistance and leukemia relapse following remissions induced by cellular immunotherapy. These studies have broad relevance for pediatric leukemias given dependencies of numerous AML and ALL subtypes upon critical oncogenic cytokine receptor signaling pathways and the demonstrated clinical efficacy of cellular immunotherapies in children with relapsed/refractory B-ALL. In this proposal, we aim to develop combinatorial CAR approaches targeting (1) the TSLP receptor plus CD19 and/or CD22 to improve remission induction and longevity in Ph-like B-ALL, (2) the FLT3 receptor plus CD19 and/or CD22 to improve remission induction and longevity in KMT2A-rearranged B-ALL, and (3) the FLT3 receptor and CD33 to improve remission induction and longevity in FLT3-mutant AML. The overall goal of these studies is to identify successful combinatorial immunotherapeutic approaches to mitigate now-known resistance mechanisms of kinase signaling and antigen escape that are imminently translatable to the clinic for early-phase testing in children with high-risk acute leukemias.